Central heating system power-flush in a very old house?

[wakemeupbefore]

What could/would go wrong?
Had some work done in one of the bathrooms, now radiators only heat partially, even after bleeding the buggers.
Power-flush suggesed but worried about flooding the house.
What should we do - or rather, have professionals do?

how old is the central-heating system?

Are the pipes copper?

Are they the size of your finger or the size of a pencil?

Do you mean all the radiators now heat, but all over; or do you mean that some of the radiators don't heat?

Is it the radiators highest in the house?

Is it the top, the middle, or the bottom of the radiators that don't heat?

Have you got a small water tank in the loft? How deep is the water? How deep is the mud?

PigletJohn, thank you for taking the time!!!

I believe the central heating was put in 40+ years ago , many pipes run above the walls and are painted the colour of the walls, sounds weird but it's not too bad.

The pipes are the size of my finger.

I believe they are copper as the old pipes taken out of bathroom were copper.

At least 1 radiator upstairs heated (when we last had heating on) from the top, bottom part staying cool.

One of the radiators downstairs wasn't heating at all after the bathroom refurbishment and plumber messed around with it for ages, finally getting it to get warmish. (At that point we were so fed up with the never-ending building work, we were glad to have some heat from it).
The said downstairs radiator then stopped heating during the winter .

I believe the chap emptied the tank in the loft and configured the pipe-work so that all cold water now comes from the mains. Not sure wheter relevant but our incoming water pressure is fierce, apparently, very high for such old property?

The radiators that heat unevenly - if I remember correctly - were not heating from different areas, some bottom, some top.

Radiators are the old cast-iron jobs, as big as the come.

so you have old iron radiators and old copper pipes.

Is there a pressure gauge on your boiler? What does it read?

You need to find out if there are any tanks still in your loft.

Did any of your radiators get fully hot?

Was the plumber a bathroom fitter or a heating engineer?